1. Field of the Invention
The invention relates to a process for treating a discoloration of an aminosilane.
2. Discussion of the Background
Organofunctional silanes are of great economic interest and currently envelop a multiplicity of industrial applications.
In particular 3-chloropropylchlorosilanes are important intermediates in the preparation of organofunctional silanes. They are generally prepared by hydrosilylation of allyl chloride. 3-Chloropropyltrichlorosilane or 3-chloropropylmethyldichlorosilane can be used to prepare, for example, 3-chloro-propyltrialkoxysilanes, 3-chloropropylmethyldialkoxysilanes and 3-aminopropyltrialkoxysilanes, such as 3-aminopropyltrimethoxysilane (AMMO) or 3-aminopropyl-triethoxysilane (AMEO); 3-aminopropylmethyldialkoxysilanes; N-aminoethyl-3-aminopropyltrialkoxysilanes, such as N-aminoethyl-3-aminopropyltrimethoxysilane (DAMO), N-aminoethyl-3-aminopropylmethyldialkoxysilanes and 2-aminoethyl-2-Nxe2x80x2-aminoethyl-3-N-aminopropyl-trialkoxysilane. The aminosilanes can be high-purity products or technical quality grades. Thus, technical quality grades also include, for example, oligomeric aminosilane fractions. The term aminosilanes thus also comprises mixtures of identical or different monomeric aminoalkoxysilanes and their oligomers and polymers in weight ratios of 0.5:99.5 to 99.5:0.5. In addition said technical quality grades of aminosilanes can also comprise what are termed bis-aminosilanes.
In addition, aminosilanes which are obtained in the manner described above generally further have an unwanted content of hydrolyzable and non-hydrolyzable chloride. The hydrolyzable chloride is also termed acid chloride.
In addition, in the case of aminosilanes, a discoloration is frequently observed which reduces the quality and restricts the potential uses for such products. Such discolorations can arise, for example, by photooxidation.
DE-A 25 21 399 discloses a process for preparing amino-alkylsilanes in which a haloalkylsilane is reacted with excess ammonia. An amount of metal alkoxide, which may be dissolved in alcohol, for example sodium methoxide in methanol, which is equivalent to the amount of chloride present in the mixture is added to the mixture produced in the amination, after filtration. In the course of everyday operations, overtitration is easily possible, so that an excess of base remains in the product.
EP-A 0 702 017 teaches removing hydrolyzable chloride from aminoorganosilanes by a targeted substoichiometric procedure using a metal alkoxide and a product-sparing working temperature.
However, to neutralize acid chloride in aminosilanes, other basic compounds can also be used, for example alkali metal or alkaline earth metal, alkali metal hydroxides or alkaline earth metal hydroxides, alkali metal carbonates or alkaline earth metal carbonates, acid or neutral or basic salts (EP-A 0 464 819), metal oxides or clay earths.
It is an object of the present invention to provide a method for reducing the discoloration of aminosilanes.
This and other objects have been achieved by the present invention the first embodiment of which includes a process for treating a discoloration of an aminosilane, comprising:
adding an acid chloride to said aminosilane having said discoloration to obtain a mixture having a molar excess of said acid chloride;
neutralizing said molar excess of said acid chloride in one or more steps with a molar deficit of a base to obtain a mixture containing a salt of said acid chloride and said base;
separating off said salt from said mixture containing said salt to obtain a treated aminosilane; and
irradiating said treated aminosilane with UV-containing light to obtain an irradiated aminosilane.